How to set material underneath a texture?
Prepare the sticker image, give it a transparent background (Alpha 0%). Select the faces where you want the sticker to be displayed, unwrap them, give them a new material.

Prepare your node setting: Create an Image Texture and load your sticker picture, plug it in a Diffuse node. Mix this Diffuse with another Diffuse node that has your object background color (red in your case).

Plug the Image Texture Alpha output in the Mix Shader Factor input so that the sticker background appears transparent.